Dry sensor circuit with static discriminator for dryer

ABSTRACT

A dry sensor circuit employs a static discriminator to prevent positive electrostatic charges carried by clothes being dried from causing erroneous signals to the dryer control circuit. The static discriminator includes a neon tube having a control electrode in the form of a metal shield which surrounds the glass envelope of the tube. The voltage level of the metal shield affects the level of the breakdown voltage of the neon tube. The shield is connected to an electrode of a dryness sensor so that positive electrostatic charges cause the shield voltage level to become positive with respect to both the cathode and the anode of the tube to lower the breakdown voltage. When the breakdown voltage decreases to a level below that impressed thereon by a voltage divider network, the neon tube fires to indicate that the static charge does not represent wet fabric.

United States Patent Marcade June 25, 1974 [75] Inventor: Roque D. Marcade, Stevensville,

Mich.

[73] Assignee: Whirlpool Corporation, Benton Harbor, Mich.

22 Filed: Mar. 15,1973

21 Appl. No.: 341,521

[52] US. Cl 34/45, 34/48, 34/55 [51] Int. Cl. F26!) 19/00 [58] Field of Search 34/55, 53, 48, 46, 45,

34/44; 307/118, 93', 317/2 R, 2 C; 324/65 R; 318/483; 328/4; 73/73; 313/201 [56] References Cited UNITED STATES PATENTS 2,914,695 11/1959 Meyer, Jr. et al. 313/201 2,947,913 8/1960 Trostler 313/201 3,199,033 8/1965 Atkins et a1. 328/5 3,271,878 9/1966 Martin 34/48 3,702,030 11/1972 Janke 34/45 3,729,833 5/1973 .lanke et a1 34/48 Primary ExaminerWilliam F. ODea Assistant ExaminerPaul Devinsky Attorney, Agent, or Firm-Hill, Gross, Simpson, Van Santen, Steadman, Chiara & Simpson [5 7] ABSTRACT A dry sensor circuit employs a static discriminator to prevent positive electrostatic charges carried by clothes being dried from causing erroneous signals to the dryer control circuit. The static discriminator includes a neon tube having a control electrode in the form of a metal shield which surrounds the glass envelope of the tube. The voltage level of the metal shield affects the level of the breakdown voltage of the neon tube. The shield is connected to an electrode of a dryness sensor so that positive electrostatic charges cause the shield voltage level to become positive with respect to both the cathode and the anode of the tube to lower the breakdown voltage. When the breakdown voltage decreases to a level below that impressed thereon by a voltage divider network, the neon tube fires to indicate that the static charge does not represent wet fabric.

7 Claims, 3 Drawing Figures DRY SENSOR CIRCUIT WITH STATIC DISCRIMINATOR FOR DRYER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to dryness sensor circuits and is particularly concerned with a dryness sensor circuit having a static discriminator to eliminate erroneous signals to the dryer control circuit.

2. Description of the Prior Art A neon lamp or tube as employed in the present invention is known per se. For example, US. Pat. Nos. 1,893,029 and 1,922,047 disclose the construction, use and mounting of neon lamps. In the first-mentioned patent, the neon lamp is employed for modulation of a signal in a signaling system. In the latter patent, the neon lamp is utilized in the RF section of a receiver for use as a demodulator.

In U.S. Pat. No. 3,729,833, Ser. No. 198,352 filed Nov. 12, 1971, issued May I, 1973' assigned to Whirlpool Corporation, Janke et al. disclose a dryness sensor circuit with static eliminating means for a dryer wherein the static eliminating means is connected to the dryness sensor for absorbing charge in response to a first polarity of static signals and supplying charge in response to the opposite polarity of static signals. This circuit does not, however, employ a three electrode breakdown device for static discrimination.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new and improved dry sensor circuit with static discrimination wherein one polarity of static charge, which electrically represents wet fabric, is employed to override the normal indication thereof to indicate a low moisture content of the fabric.

A sensor circuit includes a power supply for deriving half wave rectified DC voltage from a commercial 60 cycle AC voltage supply. The DC voltage is employed to operate a neon relaxation oscillator which pulses a transistor to indicate the moisture content of clothes being dried. The relaxation oscillator is connected to an electrode of a dryness sensor so that the moisture content of clothes bridging the electrodes of the sensor determines the number of pulses generated by the relaxation oscillator. When the number of pulses increases to approximately one per AC line cycle, a desired moisture content has been achieved. The other sensor electrode is connected to ground and the firstmentioned electrode is diode coupled to the oscillator circuit with such a polarity that negative electrostatic charges across the sensor electrodes do not affect the circuit. However, a positive electrostatic charge from the dry clothes would cause the sensor to appear as a low resistance (wet fabric) circuit and provide an erroneous indication to the relaxation oscillator. Therefore, means are provided for overriding the false indication from the positive electrostatic charge. This means is provided in the form of a neon lamp having a cathode and an anode connected in circuit between the DC supply and the pulse transistor. The neon lamp is provided with a control electrode in the form of a shield which embraces its glass envelope and which is connected to the first-mentioned sensor electrode. The voltage level of the shield determines the breakdown voltage of the neon lamp such that positive electrostatic charges decrease the breakdown voltage to effect firing of the lamp and pulsing of the transistor in place of the pulse normally provided by the relaxation oscillator so that the positive electrostatic charge does not provide an indication of wet fabric to the pulse transistor.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages of the invention, its organization, construction and operation will be best understood from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings, on which:

FIG. 1 is a perspective view, shown partially broken away, of a clothes drying appliance which may advantageously utilize the present invention;

FIG. 2 is a schematic diagram of a dryer control circuit with the dry sensor circuit of the present invention illustrated in block form; and

FIG. 3 is a schematic circuit diagram of a dry sensor having static discrimination and constructed in accordance with the principles of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, a clothes drying appliance is generally referenced l0 and comprises an enclosure cabinet 12 with a console 14 carried thereon. The console 14 houses a control device 16 for regulating the drying operation. A control knob 18 may be manipulated for selectively setting the control device 16 for various drying cycles of operation, as for example, automatic or timed drying cycles. The enclosure cabinet 12 comprises horizontal top and bottom panels 20 and 22, respectively, a pair of vertical side panels 24' (only one shown) and vertical front and rear panels 26 and 28, respectively. An access opening 30 is provided in the front panel 26 and is defined by an axially inturned flange 31. A closure door 32 cooperates with the access opening 30 for loading and unloading the dryer 10.

The dryer 10 further includes a drying container for tumbling clothes, in the form of a rotatable drum 34 housed within the cabinet 12 and extending axially from the front panel 26 to a bulkhead 36 spaced forwardly of the rear panel 28. To promote and encourage tumbling action in the clothing being dried, a plurality of circumferentially spaced baffles 78 are mounted on the inner surface of the drum 34. The drum 34 includes a radially inward extending front closure wall 41 havingan access opening 42 therein formed by means of an axially outtumed flange 43. The flange 43 provides a forwardly extending annular bearing which overlies and is suitably journaled on the complementary flange 31 of the cabinet 12. It will be apparent from the foregoing that the opening. 42 into the drum 34 and the opening 30 formed in the front panel 26 are concentric, providing access into the rotatable drum 34 from outside the cabinet 12. The drum 34'is supported at the rear by a pair of support rollers 48 (one being illustrated) mounted on the bulkhead 36. A raceway or circumferential groove 50 indented in the peripheral wall of the rear portion of the drum 34 serves as a track for the rollers 48.

A motor 52 is mounted on the bottom panel 22 in a rear comer of the cabinet 12 and rotatably drives the drum 34 by means of a drive belt 54 which extends around the periphery of and is in frictional engagement with the drum 34 and which also extends around a motor pulley 56 mounted at one end of a motor shaft 53. The other end of the motor shaft 58 drives a blower 60, arranged to circulate air through the drum 34. The blower 60 is included in a warm air system 62 positioned between the rear panel 28 and the bulkhead 36.

The bulkhead 36 serves to enclose an open-ended rear portion of the drum 34 and provides a fixed rear wall in which a pair of spaced openings are located. A first of these openings constitutes an air inlet 64, while the other opening serves as an air outlet 66. The blower 60 draws moisture-laden air from the interior of the drum 34 through the outlet 66, through a removable lint screen 68 and an air duct 70 to the blower 60, and then exhausts the air out of the cabinet 12 through an exhaust duct 72. Air exhaust from the drum 34 is re placed by ambient air entering the warm air system 62 by way of an intake opening (not shown) in the rear panel 28. The ambient air is drawn through a fresh air duct 74 and passes over a heater means 76 and into the drum through the air inlet 64. The warm air system 62 thus circulates a stream of warm air through the drum 34, subjecting clothing placed therein to a drying environment to remove moisture from the fabrics while the clothing is tumbled as the drum rotates.

in some instances it is desirable to freshen dry clothing, or air dry delicate fabrics without subjecting them to heated air. For this purpose, the warm air system 62 will operate in the manner just described; however, the heater means 76 will be rendered inoperative by an appropriate setting of the control device 16.

Referring to FIG. 2, the interior of the drum 34 is provided with a moisture sensor 100 having a pair of moisture sensing electrodes 120, 121 which are periodically bridged by the tumbling clothes load.

The moisture sensing electrode 121 is connected to ground and the moisture sensing electrode 120 is connected to a sensor circuit 101 which is operable to provide dryness signals to a dryer control circuit 123. The dryer control circuit 123 is provided with a plurality of outputs for controlling the various functional elements of the dryer. One of these outputs 124 is connected to the drive motor 52 for controlling the operation of the motor 52. Another output 125 of the control circuit 123 is connected to the heater 76 for controlling the energization thereof and th us controlling heating of the air stream 114. The control circuit 123 may be provided with other outputs including a master power control output which governs the opening and closing of the master power circuit for the machine.

The dryer control generally outlined above and illustrated in FIG. 2 is of the all electronic control circuit type as disclosed by Donald E. .lanke in his US. Pat. No. 3,702,030, but may also be an electromechanical dryer control having a timer motor, such as disclosed by Alvin J. Elders in his US. Pat. No. 3,497,964, both of which are assigned to Whirlpool Corporation, the assignee of the present invention.

FIG. 3 is a detailed schematic circuit diagram of a sensor circuit which may be employed with the dryer control circuit of FIG. 2. The sensor circuit 101 includes a power supply 126, an oscillator 127 and a static suppression circuit 128. The power supply 126 is connected to a commercial AC voltage supply by way of an input terminal 129. A capacitor 130 and a capacitor 132 may be provided for transient suppression. The power supply 126 comprises a resistor 131, a diode 133 and a Zener diode 134 which operates to supply half wave regulated voltage to the oscillator 127 and to the static suppression circuit 128. The oscillator 127 includes a pulse generator in the form of a neon lamp relaxation oscillator comprising a resistor 135 and a capacitor 136 for pulsing a neon lamp 138. The oscillator 127 is free-running and delivers pulses to the base of a transistor 140 by way of a resistor 139 one or more times for each cycle of the commercial AC wave form. The transistor 140 correspondingly supplies output pulses by way of its collector 141 to the control circuit 123 one or more times for each line cycle. This frequency of pulsing to the control circuit is highly advantageous for an electronic dryer control circuit such as disclosed in the aforementioned US. Pat. of Donald E. .lanke, No. 3,702,030, in that the control circuit of that patent utilizes a clock input which is derived from a 60 Hz line voltage to drive the first and second counters of the control circuit of that patent. Overflow operation of the second counter effects resetting of the first counter to prevent extended time accumulations. Continuous resetting of the counter second permits time accumulation by the first counter and sufficient time accumulation by the first counter provides for a time sequence of events in the control circuit. Therefore, continuous resetting of the second counter by pulses from the sensor circuit 101 indicates a desired dryness condition so that the dryer may proceed with additional segments of the drying cycle.

The moisture sensing electrode is connected to a junction 137 between the resistor and the neon lamp 138 by way of a diode 146. The sensor 100 and the resistor 135 therefore provide a voltage divider network, and the voltage at the junction 137 is dependent on the moisture content of the clothes bridging the electrodes 120, 121 of the sensor 100. The capacitor 136 is charged between the junction 137 and ground and ensures that the pulse generated by the neon lamp 138 will be of sufficient magnitude to turn on the transistor 140. Therefore, during the drying operation, the oscillator 127 is prevented from pulsing the transistor 140 whenever clothes having sufficient moisture content bridge the electrodes. ln the just-mentioned type of control circuit, the second counter would therefore continuously overflow to continuously reset the first counter and prevent time accumulation. As the clothes load becomes increasingly dry, the number of pulses produced by the oscillator 127 increases due to the resistance change of the clothes bridging the electrodes until such time as a substantially constant train of oscillator pulses is produced. Such a continuous pulse train will efiect continuous resetting of the second counter of the aforementioned control circuit and therefore permit time accumulation and a resulting termination of the drying operation to be effected in a program controlled by the first counter.

Because of the polarity of the diodes 133, 134 and 146, negative electrostatic charges contacting the sensor electrode 120 have no adverse affect on the sensor circuit. However, positive electrostatic charges carried by the drying clothes can cause erroneous signals when applied to the electrode 120. A strong positive charge applied to the electrode 120 will cause the sensor to falsely sense a low resistance (wet clothes) and therefore the voltage at the junction 137 will be low. This means that the neon lamp 138 will not fire whenever a positive electrostatic charge contacts the sensor electrode 120. if there are sufficient charges the sensor could erroneously allow the second counter to overflow and reset the first counter indicating a wet condition of the clothes. To discriminate between the wet clothes and the dry clothes with a positive electrostatic charge, the static discriminator circuit 128 is provided.

The static discriminator circuit 128 comprises a resistor 142 and a resistor 143 connected between the output of the power supply 126 and ground. A three electrode neon lamp 144 is connected between the junction of the resistors 142 and 143 and the junction between the neon lamp 138 and the resistor 139 which is connected to the base of the transistor 140. More specifically, the neon lamp 144 has a cathode electrode 150, an anode electrode 151, and a control electrode 152 which consists of a metal shield disposed about a glass envelope 153 which contains the electrodes 150 and 151 of the neon lamp 144. The voltage level of the metal shield affects the level of the breakdown voltage of the neon lamp 144. When the shield voltage level is the same as or below the voltage level of the cathode, electrode 150, the level of the neon lamp breakdown voltage is increased. When the voltage level of the shield is the same as or above the voltage level of the anode electrode 151, the level of the breakdown voltage is decreased. The resistors 142 and 143 provide a voltage divider network which biases the neon lamp 144 slightly below the normal breakdown voltage and in normal operation of the sensor circuit the neon lamp remains off because the shield voltage level is the same as or below the cathode voltage level. However, when a positive electrostatic charge comes in contact with the sensor electrode 120, the shield voltage level becomes positive with respect to the cathode and is the same as or more positive than the anode voltage level. Therefore, the breakdown voltage level of the neon lamp decreases, and is below the voltage level impressed thereon by the voltage divider network composed of the resistors 142, 143. The neon lamp 144 therefore fires, sending a pulse to the transistor 140 in place of the pulse normally sent by the lamp 138, so

that the electrostatic charge does not falsely indicate to g the control circuit a wet clothes condition.

From the foregoing it is apparent that certain advantages are derived from the present invention. For example, the static discriminator overrides false signals of the sensor circuit caused by dry clothing carrying positive electrostatic charges so that the dryness control circuit does not receive false indications that the clothes are still wet. Also, the neon lamp employed in the discriminator circuit is simple and easy to construct because the lamp essentially comprises a two electrode neon lamp with a metal shield positioned about the glass envelope.

Although I have described my invention by reference to a specific illustrative embodiment thereof, many changes and modifications of the invention may become apparent to those skilled in the art without departing from the spirit and scope of the invention. I therefore intend to include within the patent warranted hereon all such changes and modifications as may reasonably and properly be included within the scope of my contribution to the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. in a clothes dryer having a means for drying a clothes load and a moisture sensing dryer control having sensor electrodes for contacting the clothes load, said control further having a sensing circuit with generating means connected to said electrodes for generating a signal indicative of the moisture content of the clothes load and a control circuit for controlling operation of the drying means in accordance with signals received from said sensing circuit, the improvement comprising:

a static discriminator circuit connected to said electrodes and said sensing circuit including electrostatic potential sensing means connected to said generating means and operable to generate a supplemental signal upon sensing an electrostatic potential across said electrodes which is falsely indicative to said sensing circuit of a high moisture content of the clothes load, said supplemental signal being supplied to said generating means to override said false indication from said electrostatic potential across said electrodes, whereby the moisture content of said clothes load is accurately indicated by the sensing circuit.

2. In a clothes dryer having a means for drying a clothes load and a moisture sensing dryer control having sensor electrodes for contacting the clothes load, said control further having a sensing circuit connected to said electrodes for generating a signal indicative of the moisture content of the clothes load and a control circuit for controlling the operation of the drying means in accordance with signals received from said sensing circuit, the improvement comprising:

a static discriminator circuit connected to said sensor electrodes and said sensing circuit and operable to generate a supplemental signal in response to an electrostatic potential across said sensor electrodes which is falsely indicative to said sensing circuit of a high moisture content of the clothes load, said supplemental signal being supplied to said sensing circuit to override said false indication from said electrostatic potential across said sensor electrodes, said static discriminating circuit comprising a three electrode neon lamp, means connected to a first electrode of said lamp for biasing the lamp below its breakdown level, a second electrode of said lamp connected to said sensing circuit for supplying said supplemental signal thereto, and the third electrode of said lamp comprising a metal band disposed about said lamp and connected to one of said sensor electrodes for applying the electrostatic potential to said lamp to lower the breakdown level thereof, said lamp firing in response to the lowering of its breakdown level to generate said supplemental signal, whereby the moisture content of said clothes load is accurately indicated by the sensing circuit.

3. A moisture sensing circuit for supplying pulses to a dryer control circuit to indicate the moisture content of clothes being dried, comprising:

a source of DC voltage;

an oscillator connected to said source of DC voltage and including a resistor;

a moisture sensor including electrodes to be bridged by the clothes being dried and exhibiting a resistance in accordance with the moisture content of the clothes, said sensor connected to said resistor of said oscillator to form a voltage divider which controls the pulse repetition of said oscillator as the moisture content of the clothes changes; and

a static suppression circuit including a neon lamp connected to the output of said oscillator, bias means connected between said neon lamp and said source of DC voltage for biasing said lamp below its breakdown level, and means connected to one of said electrodes of said sensor and to said lamp for lowering the breakdown level of said lamp, said lamp responsive thereto to tire and cause generation of a supplemental signal at the output of said oscillator.

4. A moisture sensing circuit according to claim 3, wherein saidbias means includes a pair of serially connected resistors, said lamp connected to the junction of said resistors.

5. A moisture sensing circuit according to claim 3, wherein said means for lowering the breakdown level of said lamp comprises an electrode disposed about said lamp.

6. A moisture sensing circuit according to claim 3, wherein said lamp includes a first electrode connected to said bias means and a second electrode connected to said oscillator, and said means for lowering the breakdown level of said lamp includes a third electrode in the form of a band positioned about said lamp.

7. In a clothes dryer having a means for drying a clothes load and a moisture sensing dryer control having sensor electrodes for contacting the clothes load, said control further having a sensing circuit connected to said electrodes for generating a signal indicative of the moisture content of the clothes load and a control circuit for controlling operation of the drying means in accordance with signals received from said sensing circuit, the improvement comprising:

a static discriminator circuit including a three electrode neon lamp connected to said sensor electrodes and to said sensing circuit, means connected to said lamp for biasing said lamp below its breakdown level, said lamp operable to generate a supplemental signal in response to an electrostatic potential across said sensor electrodes which is falsely indicative to said sensing circuit of a high moisture content of the clothes load, said supplemental signal being suppled to said sensing circuit to override said false indication, whereby the moisture content of the clothes load is accurately indicated by the sensing circuit. 

1. In a clothes dryer having a means for drying a clothes load and a moisture sensing dryer control having sensor electrodes for contacting the clothes load, said control further having a sensing circuit with generating means connected to said electrodes for generating a signal indicative of the moisture content of the clothes load and a control circuit for controlling operation of the drying means in accordance with signals received from said sensing circuit, the improvement comprising: a static discriminator circuit connected to said electrodes and said sensing circuit including electrostatic potential sensing means connected to said generating means and operable to generate a supplemental signal upon sensing an electrostatic potential across said electrodes which is falsely indicative to said sensing circuit of a high moisture content of the clothes load, said supplemental signal being supplied to said generating means to override said false indication from said electrostatic potential across said electrodes, whereby the moisture content of said clothes load is accurately indicated by the sensing circuit.
 2. In a clothes dryer having a meanS for drying a clothes load and a moisture sensing dryer control having sensor electrodes for contacting the clothes load, said control further having a sensing circuit connected to said electrodes for generating a signal indicative of the moisture content of the clothes load and a control circuit for controlling the operation of the drying means in accordance with signals received from said sensing circuit, the improvement comprising: a static discriminator circuit connected to said sensor electrodes and said sensing circuit and operable to generate a supplemental signal in response to an electrostatic potential across said sensor electrodes which is falsely indicative to said sensing circuit of a high moisture content of the clothes load, said supplemental signal being supplied to said sensing circuit to override said false indication from said electrostatic potential across said sensor electrodes, said static discriminating circuit comprising a three electrode neon lamp, means connected to a first electrode of said lamp for biasing the lamp below its breakdown level, a second electrode of said lamp connected to said sensing circuit for supplying said supplemental signal thereto, and the third electrode of said lamp comprising a metal band disposed about said lamp and connected to one of said sensor electrodes for applying the electrostatic potential to said lamp to lower the breakdown level thereof, said lamp firing in response to the lowering of its breakdown level to generate said supplemental signal, whereby the moisture content of said clothes load is accurately indicated by the sensing circuit.
 3. A moisture sensing circuit for supplying pulses to a dryer control circuit to indicate the moisture content of clothes being dried, comprising: a source of DC voltage; an oscillator connected to said source of DC voltage and including a resistor; a moisture sensor including electrodes to be bridged by the clothes being dried and exhibiting a resistance in accordance with the moisture content of the clothes, said sensor connected to said resistor of said oscillator to form a voltage divider which controls the pulse repetition of said oscillator as the moisture content of the clothes changes; and a static suppression circuit including a neon lamp connected to the output of said oscillator, bias means connected between said neon lamp and said source of DC voltage for biasing said lamp below its breakdown level, and means connected to one of said electrodes of said sensor and to said lamp for lowering the breakdown level of said lamp, said lamp responsive thereto to fire and cause generation of a supplemental signal at the output of said oscillator.
 4. A moisture sensing circuit according to claim 3, wherein said bias means includes a pair of serially connected resistors, said lamp connected to the junction of said resistors.
 5. A moisture sensing circuit according to claim 3, wherein said means for lowering the breakdown level of said lamp comprises an electrode disposed about said lamp.
 6. A moisture sensing circuit according to claim 3, wherein said lamp includes a first electrode connected to said bias means and a second electrode connected to said oscillator, and said means for lowering the breakdown level of said lamp includes a third electrode in the form of a band positioned about said lamp.
 7. In a clothes dryer having a means for drying a clothes load and a moisture sensing dryer control having sensor electrodes for contacting the clothes load, said control further having a sensing circuit connected to said electrodes for generating a signal indicative of the moisture content of the clothes load and a control circuit for controlling operation of the drying means in accordance with signals received from said sensing circuit, the improvement comprising: a static discriminator circuit including a three electrode neon lamp connected to said sensor electrodes and to said sensing circuit, means connected to said lamp for biasing said lamp below its breakdown level, said lamp operable to generate a supplemental signal in response to an electrostatic potential across said sensor electrodes which is falsely indicative to said sensing circuit of a high moisture content of the clothes load, said supplemental signal being suppled to said sensing circuit to override said false indication, whereby the moisture content of the clothes load is accurately indicated by the sensing circuit. 